It is now something over fifty years since the appearance of that major landmark in liturgical history that was the Motu proprio of Pope St Pius X, Tra le sollecitudini, published on November 22, 1903. The original text was in Italian, though it was accompanied by a Latin text also. It is worth examining briefly the nature of a Motu proprio, by way of comparison with some subsequent legislation. A Motu proprio is a papal rescript, including these words ('of his own accord’), signifying that the Pope has decided personally on its provisions, neither depending upon the request or advice of others, nor setting out to deal with a particular case. (A special legal characteristic of a Motu proprio is that it does not depend for its validity upon the validity of the reasons alleged for its issue, as is the case with ordinary rescripts where the phrase is not used: the Motu proprio is valid whatever may happen to the reasons.) The most well-known Motu proprio is this one on Church Music, so that the term suggests to most people this particular document.